1. Field of the Invention
This invention relates to the field of data processing systems. More particularly, this invention relates to the field of encrypted data files and their rendering for display or playback.
2. Description of the Prior Art
With the increase in the use of e-mail as a communication mechanism, there has also been a corresponding rise in the need to send messages and data that are confidential. Various encryption techniques have been developed to address this need. Generally, these techniques involve decryption keys which are made available to the recipient at the point of receipt. These keys can be used to decrypt the message once received. This has the result that in transit the message is encrypted and thus, even if intercepted, cannot be read.
There are many encryption techniques available at present for sending someone confidential information. Such techniques often involve the use of decryption keys which can be accessed on production of the correct password. These methods provide a good level of confidentiality for the information in transit, but there are weaknesses in the system after the information has been received.
One problem with existing encryption techniques is that in many cases a decrypted message is stored and thus, even after subsequent deletion, it may be possible to restore the information at some point in the future. A further point is that although current encryption algorithms may be deemed impractical to break at the moment, in five or ten years time decryption may be possible with new computing techniques. The ability to restore the encrypted messages from archive medium may therefore also be a potential problem.
Encryption techniques are known in which the user can specify that a message be read only once. However, this does not protect it from being saved in an unencrypted form or forwarded to other users. ZipLip.com, for example, provides a read-once Web based messaging service, but the contents can be printed, copied to disk and retrieved by administrators from archive media.